Mode-switched variable signal attributes in block diagrams

ABSTRACT

A programming element is provided that defines model attributes in response to mode change events in a graphical modeling environment. Such definition may involve any signal attribute such as dimensions, data types, complexity and sample times. Events that trigger definition of model attributes may be explicit signaling events generated by other elements, elements within the block diagram programming environment, and elements external from the environment. Implicit events may also trigger definition of model attributes, such as a change of attribute in an input signal.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. 119(e) to U.S.Provisional Application Ser. No. 60/980,403, entitled “MODE-SWITCHEDVARIABLE SIGNAL ATTRIBUTES IN BLOCK DIAGRAMS,” by Ramamurthy Mani, filedOct. 16, 2007, of which application is incorporated herein by referencein its entirety.

BACKGROUND

Various classes of block diagrams may be used to describe computationsthat can be performed on application specific computational hardware,such as a computer, microcontroller, FPGA, and custom hardware orgeneral purpose hardware such as a commercially-available computersystem or microprocessor. Classes of these block diagrams can includetime-based block diagrams, such as those implemented within graphicalmodeling environments, state-based and flow diagrams, and data-flowdiagrams. Graphical modeling environments such as block diagramprogramming environments generally permit a user to define and usegraphical elements to represent system behavior. These elements may be,in one example, elements that are interconnected graphically to create arepresentation of a modeled system.

Graphical modeling environments (e.g., as provided by graphicalprogramming tools) may assist in simplifying the process of designing,simulating, and implementing dynamic systems. Tools provided in suchmodeling environments may permit a user to create a graphicalrepresentation of a system, such as a time-based block diagramrepresentation, a statistical diagram, a timing diagram, and othersimilar graphical elements that can be used to describe system behavior.

SUMMARY

According to one aspect, a computer-readable medium is providedcomprising computer-executable instructions that when executed on aprocessor propagate attributes in a graphical model. The medium includesinstructions for displaying a graphical model representing a systemconfigured to operate using a first behavior, the graphical modelcomprising a first element having a first attribute, a second element,and instructions for associating a mode switching event with the firstelement. The medium further includes instructions for propagating thefirst attribute within the first element, or propagating the firstattribute from the first element to the second element in response tothe mode switching event, and instructions for executing the graphicalmodel using the propagated first attribute to produce an executionresult that reflects a second behavior of the graphical model.

According to one embodiment, the at least one attribute comprises atleast one signal attribute that includes at least one of a signaldimension, a signal data type, a signal complexity or a signal sampletime. According to one embodiment, the medium further comprisesinstructions for selectively resetting a state associated with the atleast one element in response to the propagating the at least oneattribute. According to another embodiment, the mode switching eventincludes an explicit event or an implicit event.

According to another embodiment, the mode switching event is generatedby at least one of a state transition diagram, a discrete event diagram,or a block diagram. According to another embodiment, the first elementincludes at least one port, and wherein the mode switching event is inresponse to a change in attribute of a received signal associated withthe at least one port. According to another embodiment, the graphicalmodel includes at least one of a time-based block diagram or a dataflowdiagram.

According to one embodiment, the medium further comprises instructionsfor indicating that the at least one element propagates the at least oneattribute in response to the mode switching event. According to oneembodiment, the medium further comprises instructions for receiving aflag, the flag indicating that the first element can process the modeswitching event.

According to another embodiment, the first element includes at least oneinput port and at least one output port, and wherein the first attributeis a dimension, and wherein the computer-readable medium furthercomprises instructions for receiving a map defining at least oneconstraint, the constraint identifying a dimension of the at least oneinput port, the dimension used to determine a dimension of the at leastone output port, and instructions, responsive to a selection of the atleast one constraint, for setting the dimension of the at least oneoutput port based on the selected at least one constraint.

According to another aspect, a computer-readable medium is providedcomprising computer-executable instructions that when executed on aprocessor modify an operating mode for a system. The medium includesinstructions for operating the system in a first mode having a first setof behavior, instructions for receiving a mode switching event,instructions for operating the system in a second mode having a secondset of behavior based on the received mode switching event, andinstructions, responsive to receiving the mode switching event, forexecuting the instructions for operating the system in the second mode.

According to one embodiment, the computer-executable instructions aregenerated from a graphical model representing a modeled system.According to another embodiment, the graphical model comprises a firstelement having a first attribute and a second element, and wherein thecomputer-readable medium further holds instructions for associating themode switching event with a first element of the graphical model, andinstructions for propagating the first attribute within the firstelement, or propagating the first attribute from the first element tothe second element in response to the mode switching event.

According to another embodiment, the first set of behavior is operableto permit the system to process a first set of conditions by the system,and wherein the second set of behavior is operable to permit the systemto process a second set of conditions by the system. According toanother embodiment, the instructions responsive to receiving the modeswitching event are executed by the system at runtime.

According to another embodiment, the graphical model comprises a firstelement including at least one input port and at least one output port,and wherein the computer-readable medium further comprises instructionsfor receiving a map defining at least one constraint, the constraintidentifying a dimension of the at least one input port, the dimensionused to determine a dimension of the at least one output port, andinstructions, responsive to a selection of the at least one constraint,for setting the dimension of the at least one output port based on theselected at least one constraint.

According to another embodiment, the graphical model comprises a firstelement having a first attribute, and wherein code associated with thefirst element is responsive to the received mode switching event.According to another embodiment, the code associated with the firstmodel is capable of propagating the first attribute in response to thereceived mode switching event. According to another embodiment, the codeis adapted to propagate the first attribute during execution of thecode.

According to another aspect, a system is provided comprising a memoryconfigured to store code representing a graphical model representing amodeled system, the graphical model having at least one element havingassociated code that is configured to propagate, through the element orto another element, at least one attribute associated with a port of theelement, and a processor configured to execute the code, and responsiveto a mode switching event, propagates the at least one attribute.According to one embodiment, the system operates in a first mode havinga first set of behavior, and in response to receiving the mode switchingevent, the system operates in a second mode having a second set ofbehavior. According to another embodiment, the mode switching event isin response to a change in attribute of a received signal associatedwith the port of the element.

According to another aspect, a computer-readable medium is providedcomprising computer-executable instructions that when executed on aprocessor determine attributes in a graphical model. The medium includesinstructions for displaying a graphical model representing a systemconfigured to operate using a first behavior, the graphical model havinga fixed model variable access structure and comprising a first elementhaving a first attribute, a second element having a second attribute,and instructions for associating a mode switching event with the firstelement, instructions for determining the second attribute to beconsistent with the first attribute, the instructions for determiningbeing responsive to the mode switching event, instructions for executingthe graphical model using the determined second attribute to produce anexecution result that reflects a second behavior according to the secondattribute of the graphical model.

According to one embodiment, the fixed model variable access structureis a fixed read structure. According to another embodiment, the fixedmodel variable access structure is a fixed write structure. According toanother embodiment, the fixed model variable access structure is a fixedread and write structure. According to another embodiment, the fixedmodel variable access structure is a fixed compile-time structure.According to another embodiment, the instructions for determiningpropagate the first attribute to the second attribute. According toanother embodiment, the instructions for determining further compriseinstructions for solving at least one constraint associated with thefirst attribute and at least one constraint associated with the secondattribute.

According to one embodiment, the at least one constraint associated withthe first attribute and the at least one constraint associated with thesecond attribute are related. According to another embodiment, the atleast one constraint associated with the first attribute and the atleast one constraint associated with the second attribute are a sameconstraint. According to another embodiment, the first element and thesecond element are not directly connected. According to anotherembodiment, the first element and the second element are connected via anondirect feedthrough element. According to another embodiment, thenondirect feedthrough element comprises an input and an output, andwherein the nondirect feedthrough element does not have a directrelationship between the input and the output. According to anotherembodiment, the nondirect feedthrough element includes at least one of agroup comprising a delay element, a pre element, a shift element, and amemory element. According to another embodiment, the nondirectfeedthrough element includes a filter block.

According to another embodiment, the instructions for determining thesecond attribute include instructions that permit the user to define aprocess by which the second attribute is determined. According toanother embodiment, the computer-readable medium further comprisesinstructions that, when executed, display to a user an option to selecta functionality that determines the second attribute responsive to themode switching event. According to another embodiment, the at least oneattribute comprises at least one signal attribute that includes a signaldimension. According to another embodiment, the at least one attributecomprises at least one signal attribute that includes a signal datatype.

According to one embodiment, the at least one attribute comprises atleast one signal attribute that includes a signal complexity. Accordingto another embodiment, the at least one attribute comprises at least onesignal attribute that includes a signal sample time. According toanother embodiment, the at least one attribute comprises at least onesignal attribute that includes a signal invocation specification.According to another embodiment, the computer-readable medium furthercomprises instructions for selectively resetting a state associated withthe at least one element in response to the instructions for determiningthe at least one attribute.

According to another embodiment, the mode switching event includes anexplicit event. According to another embodiment, the mode switchingevent includes an implicit event. According to another embodiment, themode switching event is generated by at least one of a state transitiondiagram, a discrete event diagram, a block diagram, a dataflow diagram,sequence diagram, scenario diagram, truth table, state transitionmatrix, entity flow diagram, queue/server network, and function blockdiagram. According to another embodiment, the first element includes atleast one port, and wherein the mode switching event is in response to achange in attribute of a received signal associated with the at leastone port.

According to one embodiment, the graphical model includes at least oneof a time-based block diagram, activity diagram, or a dataflow diagram.According to another embodiment, the computer-readable medium furthercomprises instructions for indicating that the at least one elementpropagates the at least one attribute in response to the mode switchingevent. According to another embodiment, the computer-readable mediumfurther comprises instructions for receiving a flag, the flag indicatingthat the first element can process the mode switching event. Accordingto another embodiment, the first element includes at least one inputport and at least one output port, and wherein the first attribute is adimension, and wherein the computer-readable medium further comprisesinstructions for receiving a map defining at least one constraint, theconstraint identifying a dimension of the at least one input port, thedimension used to determine a dimension of the at least one output port,and instructions, responsive to a selection of the at least oneconstraint, for setting the dimension of the at least one output portbased on the selected at least one constraint.

According to one aspect of the present invention, a computer-readablemedium comprising computer-executable instructions that when executed ona processor modify an operating mode for a system, thecomputer-executable instructions being generated from a graphical modelrepresenting the system, the graphical model having a fixed modelvariable access structure is provided. The medium includes instructionsfor operating the system represented by the graphical model in a firstmode having a first behavior, instructions for receiving a modeswitching event, instructions for operating the system in a second modehaving a second behavior based on the received mode switching event, andinstructions, responsive to receiving the mode switching event, forexecuting the instructions for operating the system in the second mode.According to one embodiment, the graphical model comprises a firstelement having a first attribute and a second element, and wherein thecomputer-readable medium further holds instructions for associating themode switching event with a first element of the graphical model,instructions for representing a first element having a first attribute,instructions for representing a second element having a secondattribute, and instructions for associating a mode switching event withthe first element, instructions for determining the second attribute tobe consistent with the first attribute, the instructions for determiningbeing responsive to the mode switching event.

According to another embodiment, the fixed model variable accessstructure is a fixed read structure. According to another embodiment,the fixed model variable access structure is a fixed write structure.According to another embodiment, the fixed model variable accessstructure is a fixed read and write structure. According to anotherembodiment, the fixed model variable access structure is a fixedcompile-time structure.

According to one embodiment, the instructions for determining areadapted to propagate the first attribute to the second attribute.According to another embodiment, the instructions for determiningfurther comprise instructions for solving at least one constraintassociated with the first and second attributes. According to anotherembodiment, the first element and the second element are not directlyconnected. According to another embodiment, the second element includesa nondirect feedthrough characteristic. According to another embodiment,the first element and the second element are connected via a nondirectfeedthrough element. According to another embodiment, the nondirectfeedthrough element comprises an input and an output, and wherein thenondirect feedthrough element does not have a direct relationshipbetween the input and the output.

According to another embodiment, the nondirect feedthrough elementincludes a delay block. According to another embodiment, the nondirectfeedthrough element includes a memory block. According to anotherembodiment, the instructions for determining the second attributeinclude instructions that permit the user to define a process by whichthe second attribute is determined. According to another embodiment, thecomputer-readable medium further comprises instructions that, whenexecuted, display to a user an option to select a function thatdetermines the second attribute responsive to the mode switching event.

According to one embodiment, the first behavior is operable to permitthe system to process a first set of conditions by the system, andwherein the second behavior is operable to permit the system to processa second set of conditions by the system. According to anotherembodiment, the instructions responsive to receiving the mode switchingevent are executed by the system at runtime. According to anotherembodiment, the graphical model comprises a first element including atleast one input port and at least one output port, and wherein thecomputer-readable medium further comprises instructions for receiving amap defining at least one constraint, the constraint identifying adimension of the at least one input port, the dimension used todetermine a dimension of the at least one output port, and instructions,responsive to a selection of the at least one constraint, for settingthe dimension of the at least one output port based on the selected atleast one constraint. According to another embodiment, the graphicalmodel comprises a first element having a first attribute, and whereincode associated with the first element is responsive to the receivedmode switching event. According to another embodiment, the codeassociated with the first model is capable of propagating the firstattribute in response to the received mode switching event. According toanother embodiment, the code is adapted to propagate the first attributeduring execution of the code.

According to one aspect of the present invention, a system comprises amemory configured to store information representing a graphical modelrepresenting a modeled system, the graphical model having a fixed modelvariable access structure and including at least one element, the atleast one element having associated code that is configured to make atleast one attribute associated with a port of the element consistentanother attribute of the at least one element or another element, and aprocessor configured to execute the code, and responsive to a modeswitching event, defining the at least one attribute to be consistentwith the another attribute. According to one embodiment, the systemoperates in a first mode having a first behavior, and in response toreceiving the mode switching event, the system operates in a second modehaving a second behavior. According to another embodiment, the modeswitching event is in response to a change in attribute of a receivedsignal associated with the port of the element. According to anotherembodiment, the attribute is propagated through the at least one elementor to another element. According to another embodiment, the fixed modelvariable access structure is a fixed read structure. According toanother embodiment, the fixed model variable access structure is a fixedwrite structure. According to another embodiment, the fixed modelvariable access structure is a fixed read and write structure. Accordingto another embodiment, the fixed model variable access structure is afixed compile-time structure.

Further features and advantages as well as the structure and operationof various embodiments are described in detail below with reference tothe accompanying drawings. In the drawings, like reference numeralsindicate like or functionally similar elements. Additionally, theleft-most one or two digits of a reference numeral identifies thedrawing in which the reference numeral first appears.

BRIEF SUMMARY OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that is shown invarious figures may be represented by a like numeral. For the purpose ofclarity, not every component may be labeled in every drawing. In thedrawings:

FIG. 1 shows an example system that can be modeled using modelingsoftware;

FIG. 2 shows a conventional technique for varying signal sizes thatchange in synchrony with a control signal;

FIG. 3 shows one application that may be modeled using an exemplaryembodiment;

FIG. 4 shows an example system that exhibits shortcomings ofconventional modeling systems;

FIG. 5A shows one example system in which various aspects may bepracticed;

FIG. 5B shows an example block diagram implementation of the systemshown in FIG. 5A;

FIG. 6A shows an example block implementing various aspects ofpropagating parameters in a modeled system;

FIG. 6B shows an example subsystem implementing various aspects ofpropagating parameters in a modeled system;

FIG. 7 shows an example subsystem that is responsive to mode changeevents;

FIG. 8 shows an example state diagram that includes a state model thatchanges modes in response to mode change events;

FIG. 9 shows an example graphical programming environment in whichvarious aspects may be practiced;

FIGS. 10A-10B show processes for performing a design and execution of agraphically-modeled system according to one embodiment; and

FIG. 11 shows a general-purpose computer system suitable for practicingexemplary embodiments.

DETAILED DESCRIPTION

As discussed, graphical modeling languages (e.g., a graphicalprogramming language such as a block diagram programming language) maybe used to model a program. Graphical modeling languages may benefitfrom elements (e.g., block diagram elements) that can operate indifferent modes. For instance, elements of the block diagram may exhibitdifferent behavior when functioning in different modes. In some blockdiagrams, it may be beneficial to have the ability to process differenttypes of data, and it may be beneficial to modify the execution behaviorof one or more elements of the diagram when the different types of dataare changed.

Conventional techniques of graphical programming have elements that arelimited in their function during execution points where attributes suchas dimension, initial conditions, and complexity are changed. Forinstance, a sum block that computes the sum of two inputs may beprovided in a model of a system. When a dimension of one of the inputsof the sum block does not match a dimension on one of the other inputbecause of a change in input signal dimensions, an error may occurbecause of the difference in signal dimensions and the inability of theelement to resolve such a difference.

Further, it is appreciated that conventional techniques for graphicalprogramming are limited in that some types of elements, such as elementsnot having a direct feedthrough, are incapable of directly relating aninput to an output, and mode changes involving signal attributes areincapable of traversing elements having nondirect feedthroughcharacteristics. As defined herein, a direct feedthrough of an elementrelates an input of the element to an output of the element. A directfeedthrough need not relate all inputs to outputs, but elements may haveinputs that have direct feedthrough. In one example, in a lazy (ordelayed) evaluation scheme, the output of a function may be computedwithout the need to have all input values available.

The direct relation could be between one or more of the element inputvalues and one or more of the element output values. In case of portbased input and output, the direct feedthrough could be differentiatedbetween pairs of input port and output port. If the ports have sizes ordimensions larger than 1, the direct feedthrough could be differentiatedpairwise between respective elements or sets of elements of the inputand output ports. The relation between input and output values could bean instantaneous relation. For instance, the instantaneous relationcould be a functional relation that relates an input value to an outputvalue, such as an algorithmic relation. Other functional relations couldbe used, such as an equality (e.g., as represented by an algebraicequation).

Nondirect feedthrough between a pair of variable values of an elementindicates that there is no direct relation between the pair of variablevalues. A nondirect feedthrough element may have no direct feedthroughbetween any permutation of input/output pairs. Examples of nondirectfeedthrough elements includes delay blocks, shift blocks, memory blocks,and other types of elements that do not relate input vales to outputs.In another example, there exists an element (e.g., a block) having a‘pre’ operator that prepends a sequence of values with an initial value.This ‘pre’ operator is also an example of an entity that has nondirectfeedthrough characteristics. Also, there may be elements that havenondirect feedthrough characteristics for certain input/output pairs.Because there is no direct relation between input values (or otherattributes) of some types of elements used in graphical programming,there is difficulty using conventional programming methods for modelingmode changes using such nondirect feedthrough elements.

Many types of systems may include elements that can act upon differenttypes of signals having parameters that can change dimension, data type,etc. An exemplary embodiment can include a programming element having afixed model variable access structure that handles changes inattribute(s). A model variable access structure includes the structureof read and write access of variable of a model. Access functionality ofa variable may include, for example, equations, assignments, functions,procedures, and methods.

In one embodiment, the model may have a fixed write structure, where thefunctionality that writes to a variable does not change duringexecution. In another embodiment, the model may include a fixed readstructure, where the functionality that reads a variable does not changeduring execution. Further, in another embodiment, the model includes afixed read/write structure, where the functionality that writes avariable and the functionality that reads a variable does not changeduring execution. A compile-time read and/or write structure that isfixed means that the functionality that reads and/or writes a variableduring execution does not change when the model is compiled. Thus, thefixed nature of the read/write ensures computational causality.Computational causality refers to an order of computations that can bedetermined. So, a write may be determined to always or necessarily occurbefore a read or vice versa. This implies a causal relation between theread and write in terms of their computation, hence, computationalcausality. A block diagram may be computationally causal and noncausal.In case of the latter, the block diagram may be a graphicalrepresentation of a system differential and algebraic equations.

According to one embodiment, the model can propagate changed attributesto other elements as appropriate. Such a propagation of attributes mayensure consistency among the other elements that operate in differentmodes. In one example system, an element (e.g., a block) having a fixedread/write structure may be provided that is responsive to a change inattributes, and modifies its execution behavior as a result. Forinstance, one type of element that may be responsive to mode changesincludes a nondirect feedthrough element.

In one example implementation, the amount of code necessary to implementthese elements in a block diagram programming environment may be reducedbecause elements used in exemplary embodiments can respond to changes inattributes. For instance, by having elements that operate in differentmodes, the complexity of a system design is reduced, as alternativeportions of a design that support behavior in different modes are notnecessary. Thus, system behavior may be represented (e.g., in a blockdiagram) in a more general way, and using less elements (e.g., in ablock diagram).

Block diagram environments may include block diagrams having blocks thatsupport signals having a variety of functional signal attributes. Forexample, a gain block may support n-dimensional signals with eachdimension being of any size, a range of data types, real, imaginary, andcomplex signals, a variety of both continuous and discrete sample times,etc. These functional attributes can modify the semantics or functionalbehavior of a graphical model (e.g., a block diagram, state diagram,data flow diagram, etc.). Further, blocks may be arranged to representand model systems or portions of systems (e.g., subsystems). Also,systems may be hierarchically arranged such that subsystems may containone or more blocks arranged in a block diagram.

In an exemplary embodiment, signal attributes for an instance of a blockmay be finalized (or fixed) prior to executing a block diagram. Forinstance, an embodiment may compile the diagram prior to executing thediagram. Compiling the diagram may include propagating signal attributesto a given block from all other blocks that are connected to this block.The compiler may create instances of each block of the block diagram,including the possible behavior that each block may exhibit duringruntime. In this way, blocks may be defined that exhibit polymorphicbehavior during runtime (e.g., exhibit different context-dependentbehavior during runtime). Generally, polymorphism behavior is determinedduring design time, as all possible behavior is determined duringcompilation and incorporated in an element. This concept is illustratedin FIG. 1.

FIG. 1 includes sum block 101, gain block 102, sine block 103, constantblock 104 and sink 105. Sum block 101 can include logic that adds two ormore input signals together to yield a summed output signal. Gain block102 may include logic that amplifies a received signal by a gain valueto yield an amplified output signal. Sine block 103 can include logicthat generates data values that can represent a waveform, such as asinusoidal waveform. Constant block 104 may include logic that yields avalue, such as a fixed value. Sink 105 may include logic that receivesone or more signals and stores the signals to memory and/or makes thesignals available to another type of logic, such as another model,another device, etc.

In the embodiment of FIG. 1, sum block 101, gain block 102, sine block103, constant block 104 and output 105 may operate on signals having oneor more dimensions. For example, sine block 103 may generate a signalrepresented by a 3×3 matrix, as denoted by [3×3] at the output of sineblock 103. In another embodiment, blocks may operate with vectors havinga dimension of 1×n. In the embodiment of FIG. 1, blocks that aredownstream in connectivity from another block may inheritcharacteristics from the upstream block. It should be appreciated thatcharacteristics may be inherited in any direction ofconnectivity—constraints may be defined for one element, fed to otherelements, and these constraints may be solved for a designed system.According to one embodiment, constraints may be determined for elementsof a designed system and solved based on the element connectivity withinthe designed system.

For example, sum block 101 may inherit characteristics, such as a datasize from sine wave block 103 and/or constant block 104. By way ofexample, sum block 101 inherits its data size ([3×3]) from sine waveblock 103 and constant block 104, which both yield 3×3 outputs that areprocessed by sum block 101. Further, sum block 101 yields an output(also with a dimension of [3×3]) that is provided as an input to gainblock 102. In this example, gain block 102 can inherit its data sizefrom sum block 101, which is upstream from gain block 102. In anotherembodiment, gain block 102 can inherit its signal dimensions from otherblocks in the model, such as sine wave block 103, etc. Output 105 (Out1)may inherit its size from gain block 102.

Conventional block diagram programming implementations may allowdimension attributes of a signal to vary at run-time. For example, adimension attribute may vary at every time instant with the values ofthe signal. FIG. 2 includes one example system 200 showing an effect ofvarying signal sizes or “variable sizing” during runtime.

System 200 includes a switch control 201 block that includes logic thatswitches an input signal to an output port responsive to an input signalIn1 202. As shown in FIG. 2, switch control 201 accepts input signalsConstant 203 and Constant2 204 and provides either signal as an input togain block 205 depending on the value of signal 202. Gain block 205 mayinclude logic that amplifies a received signal by a gain value to yieldan amplified output signal similar to gain block 102. Further, theoutput of gain block 205 is provided as an output signal Out1 206.

Thus, system 200 yields an output signal dimension that is dependentupon a control signal. In particular, output signal dimension of switchcontrol block 201 has a dimension of either [10] or [2] based uponwhether a control signal value provided at input port In1 202 has avalue of 0 or 1. In this form of variable sizing, signal sizes vary insynchrony with the values of the signal. For example, in FIG. 2, thesignal size provided at the output of switch control 201 (eitherdimension [2] or [10]) is modified synchronously with the value of thecontrol signal provided at input port In1 202.

FIG. 3 shows an illustrative example application in the radar signalprocessing domain in which various aspects may be implemented. In FIG.3, attributes of signals, e.g., signal dimensions, may need to be variedat run time at distinct points in the execution of the block diagram.These signal dimensions may be varied asynchronously with respect tovalues of the signal. For example, one type of asynchronous signaldimension variation may occur when signal dimensions are varied atdistinct mode-switching events.

FIG. 3 shows an image formation section 300 of a synthetic apertureradar (SAR) system that is used to perform post-processing of radarsignals using Fourier transform techniques. In one example, section 300takes raw radar signal data and yields image data. Section 300 mayinclude a Fourier Transform block 301 that includes logic that performsa Fast Fourier Transform (FFT) of an input signal s(t,u). An output ofFFT block 301 is provided as an input to a matched filter block 302 thatincludes filter logic that performs filtering of the FFT output. Thefiltered output may be provided as an input to an interpolation block303, an output of which may be provided to a block 304 that includeslogic capable of performing an inverse fast Fourier Transform (IFFT) onthe input signal.

According to one embodiment, input signal sizes in this system s(t,u)may be varied in distinct steps (e.g., 128 time points, 256 time points,etc.) to account for changes in radar resolution. Such changes inresolution may happen upon mode-switching events in the system. Changesin signal sizes need to be propagated from the input to FFT 301, matchedfilter block 302, interpolation block 303, and IFFT block 304. In thisexample shown in FIG. 3, when the sizes of signals change because of amode switch, all states in the subsystem may be reinitialized. Althoughthe functions shown in FIG. 3 are provided by way of example, suchfunctions may be any type of function having any degree of complexity.

In one embodiment, varying dimensions in synchrony with values ofsignals may be insufficient to solve certain problems, such as problemsinvolving changes to attributes such as dimensions at distinctmode-switching events. This problem is illustrated in more detail in theexample shown in FIG. 4. An example system 400 includes an input u(403), a delay block 401, a sum block 402, gain block 404, and output y(405). Unit delay block 401 may include logic that yields a one-stepdelay from input to output. Unit delay block 401 may be configured in afeedback path and provide an input to sum block 402. Gain block 404 maytake an output signal of sum block 402 and may amplify the output signalby a gain value to yield an amplified output signal. This amplifiedoutput signal may be provided as an output y (405), and also may beprovided as an input to unit delay block 401 in the feedback path.

System 400 may be executed in graphical programming environments bydetermining that, for example, delay block 401 can yield output valuesat any given time independent of an input. Therefore, the output ofdelay block 401 can be computed first, followed by the output of sumblock 402.

Now consider the case where input signal u (item 403) of system 400changes its dimensions to a new value. If signal dimensions are allowedto change only synchronously with the signal values, the output of delayblock 401 may need to be computed at a time when its input dimensions(which are the same as the output dimensions of sum block 402) have notyet been set to the new value. This is problematic, as an error mayoccur if the dimensions of the inputs of sum block 402 do not match, andblock 402 does not have the capability of processing the mismatchedinputs. This same problem extends to many different block types. Forexample, this problem applies to block types having states stored insideof them (e.g., filter blocks).

In some applications, it may be desirable to use signals whose sizessynchronously change with their values along with signals whose sizeschange on distinct mode-switching events. FIGS. 5A-5B show an exampleapplication that demonstrates a modeling problem that can arise in thewireless communications area. In particular, FIG. 5A shows acommunication system having a base station 501 that communicates withone or more transmitters/receivers 502A-502C. Wireless communicationsystems such as cellular telephone systems may have such a communicationsystem configuration. In the example shown, such a system may include acell tower that communicates with one or more cellular phones thattransmit and receive information to/from the cell tower.

In such communication system types, transmitters/receivers are added andsubtracted from the system as these transmitters/receivers are turnedon/off, enter/leave from the transmission area, or travel to variouslocations within the transmission area. One problem with maintainingcommunication in such a communication system includes determining acommunication solution that ensures diversity among thetransmitters/receivers such that as transmitters/receivers are added,communication parameters are adjusted to minimize interference betweenthe transmitters/receivers. To solve this problem, transmitter powercontrol algorithms may be provided to allow transmitters/receivers todynamically share bandwidth of a wireless channel, optimizing thechannel throughput.

FIG. 5B shows a block diagram of a system 500 that computes the powercontrol strategy for a communication system such as that shown in FIG.5A. Similar to other block diagram models, system 500 may include blockshaving logic that perform various functions. System 500 includes a block505 that represents one or more mobile stations that yield transmissionsignals [N×M]. Such signals are added via a summation block 506, and areadded to an additive white Gaussian noise channel model block 507 outputvia a sum block 508. An output of sum block 508 is provided to receiversblock 509 of a base station 510 (e.g., of base station 501) to receiveand process the received signal. Also, such a received signal isprovided to a power control block 504 that determines a power controlstrategy based on the received signal.

As shown in FIG. 5B, a closed-loop power-control strategy implemented inthe communications base-station 501 is varied at distinct points in timerather than at all times. In particular, base-station 501 feeds backinformation to the transmitters/receivers (e.g., transmitters/receivers502A-502C of FIG. 5A), to permit the transmitters/receivers to transmitat the proper frequencies/power scenarios to ensure signal diversity.System 500 may also include a bit error rate calculator 511 thatdetermines error rates within the received signal.

Although the transmission solution is computed at distinct points, thenumber of wireless transmitters/receivers (e.g., transmitters/receivers502A-502C) may change periodically over time. Mode1 500 includes signalsrepresenting transmitters/receivers (e.g., transmitters/receivers502A-502C) whose sizes change constantly in synchrony with the signalvalues. Such signal values, may be, for example, signals transmitted bytransmitters/receivers 502A-502C of FIG. 5A. In contrast, power-controlsubsystem 504 in base station 501 may use signals whose sizes change atdistinct points in time where the number of current transmitters issampled and held for the duration of time over which that power-controlstrategy is in effect. That is, for a particular time interval, thepower control strategy is maintained, although transmitters/receiversmay appear or disappear over time during any period the power controlstrategy is operating.

In the example of FIGS. 5A and 5B other signal attributes such as datatypes may also need to be varied at mode switching events. For instance,in the communication example above, different communication protocolsmay be associated with different modes, and various receivers may usedifferent protocols depending on their mode. Other system examples maybe used wherein other attributes may be varied responsive to modeswitching event. In another example using a control system involving oneor more sensor inputs, the same control strategy may need to beexercised with different data types at run-time based on switching todifferent precisions of sensor inputs.

Example Implementation

In one example implementation a mode-switched variable signal sizingblock diagram environment may be implemented using the Simulink®software product provided by The MathWorks Inc. of Natick, Mass.According to one embodiment, a block may be provided that is designed tosupport mode-switched variable size computation.

FIG. 6A shows one example block that is capable of performingmode-switched computation according to one embodiment. In particular,FIG. 6A shows a block 601 that includes code that is responsive to amode switching event. According to one embodiment, the block (or othertype of graphical modeling construct) includes code that is capable ofbeing executed by a system, permitting that system to be responsive to amode switching event. Such code may be simulated or otherwise executed(e.g., by a simulation engine, device, etc.), to respond to the modeswitching event and modify the execution behavior of one or more blocks.

Block 601 may include one or more inputs (e.g., inputs 602, 603) and mayinclude one or more outputs (e.g., output 604). In one exemplaryembodiment, block 601 may compute a sum of signal inputs 602 and 603,and yield a corresponding output 604 that represents the sum of thesignal inputs 602 and 603. In another embodiment, block 601 mayimplement other types of functions. For instance, block 601 mayimplement a concatenate function that concatenates multiple inputvectors into a single output vector. Also, blocks supportingmode-switched functions may have more or fewer inputs and/or outputs.

Block 601 may be configured to provide several types of information tothe block-diagram modeling environment. For instance, block 601 mayprovide:

(1) A flag indicating a readiness of block 601 to support mode-switchedvariable size signals. Such a flag may be made available to anotherblock, device, simulation engine, or subsystem to determine whetherblock 601 supports mode-switched variable size signals.

(2) A map that defines a set of dependency constraints on which inputport dimensions are needed for setting respective ones of its outputport dimensions. In another embodiment, an output port dimension can beused to set an input port dimension. According to one embodiment, morethan one constraint set may be specified for one output port of a block.Such a map may reside in the block (e.g., block 601) or may be definedelsewhere, such as in an external block or subsystem, in a mapassociated with a block diagram, or in any other location.

(3) A new method defined for a block, called during runtime, that setsthe sizes of each of the block's output ports based on one of thedependency constraints chosen by the simulation engine from among theconstraints provided by the block in (2).

Two code examples below demonstrate how a block (e.g., block 601) canspecify its mode-switched variable size behavior. The first exampleinvolves a 2-input sum block (e.g., block 601) that may be used in agraphical programming environment (e.g., within an environment providedby the Simulink® software product). In one embodiment, the block may usea technique to indicate its readiness to handle mode-switchedvariable-size signals. For example, in one embodiment, the block may seta flag to indicate its readiness to handle mode-switched variable-sizesignals. This flag may also be used to identify whether the block iscapable of handling mode-switched operation.

According to one embodiment, the block may also provide the followingmap in a suitable data-structure (e.g., a data structure internal to theblock or external to the block):

Constraint1: Sizes of Output1 of sum can be computed using sizes frominput 1

Constraint2: Sizes of Output1 of sum can be computed using sizes frominput 2

The block may have any number of constraints that define whatrelationship(s) need to be satisfied.

Further, according to one embodiment, the block may have associated withit code that implements a behavior resulting from a mode-switchingevent. For example, the code, when executed, may perform an attributesetting function based on a mode-switching event. In one example, thesum block may register a function with a simulation engine (e.g., asimulation engine of the Simulink® software product) of the form:

void SumSetOutputSizes(BlockHandle bh, int constraintIdx) {   if(constraintIdx == 1) {     bh->setOutputSizes(1, bh->inputSizes(1));//Copy sizes from // inp 1 to output 1   } else {     Assert(constraintIdx== 2);     bh->setOutputSizes(1, bh->inputSizes(2));// Copy sizes from// inp 2 to output 1   } }

In the example code above, the output port size dimension (e.g., ofoutput port 604) is changed to the dimension of either of the inputports (e.g., input ports 602, 603) of the sum block. The simulationengine may call the above method with either constraint index based upona propagation sequence.

As discussed, although such mode switching may be performed with a sumblock, other functions may be performed by block 601 that are responsiveto mode-switching events. The second example illustrates block 601performing a different function, namely a 2-input vector concatenation.In one embodiment, the block concatenates two input vectors into asingle output vector. As discussed above with respect to the 2-port sumblock example, the 2-input vector concatenate block may be programmed toset a flag indicating its readiness to handle mode-switchedvariable-size signals. According to one embodiment, the 2-inputconcatenate block may then provide the following map in a suitabledata-structure:

Constraint1: Sizes of Output1 of Concatenate can be computed using sizesfrom inputs 1 and 2

That is, the constraint indicates that the size dimension may bedetermined based on both of the available inputs to the concatenateblock.

Finally, the concatenate block may register a function with thesimulation engine of the form:

void ConcatSetOutputSizes(BlockHandle bh, int constraintIdx) {assert(constraintIdx == 1); // Set output size to be sum of input sizesbh->setOutputSizes(1, bh->inputSizes(1) + // ‘+’ operatorbh->inputSizes(2)); // overloaded to add // sizes of all dimensions }

As discussed above, graphical models (e.g., a block diagram model) mayinclude a number of blocks that operate in different ways. In someembodiments, it may be desirable to arrange the blocks based onfunctionality or other characteristics. One way to arrange the blocksbased on functionality or characteristics is via subsystems. In anotherembodiment, subsystems (or portions thereof) may also be adapted tosupport mode-switched processing. FIG. 6B shows an example subsystem 610that may be used to practice various embodiments.

According to one embodiment, it may be useful to identify subsystemsthat are capable of supporting mode-switched variable signal sizes.Indicators may be used to demarcate regions of the block-diagram (e.g.,a subsystem) where mode-switched variable size signals are supported.Regions may be demarcated, for example, using graphical indications,colors, or other indicator types.

A subsystem 610 that supports mode-switched processing may include oneor more blocks, each having one or more inputs and outputs. Subsystem610 may include, for example, a sum block 611, gain block 613, delayblock 612, gain blocks 614, 615 and a vector concatenate block 616. Sumblock 611 is a three-port sum block that includes logic that yields anoutput sum of the three input signals. A vector concatenate blockincludes logic that concatenates signals provided at its inputs tocreate a contiguous output signal.

Further, subsystem 610 may include one or more inputs such as inputsIn1-In4 (elements 617-620). Subsystem 610 may also include one or moreoutputs such as, for example, Out1-Out2 (elements 621-622). Theseblocks, inputs and outputs may be connected in various ways viainterconnecting signal lines, including the example arrangement shown inFIG. 6B. According to one embodiment, one or more blocks in FIG. 6B maybe adapted to perform mode-switched processing. For instance, sum block611 could be adapted to support mode-switched processing as discussedabove with respect to the example code.

According to one embodiment, subsystem 610 may be configured to processvariable size signals and to respond to one or more mode switchingevents. For instance, an event may be triggered that causes a modeswitch to be performed during processing of subsystem 610, after whichattributes are propagated among elements of subsystem 610.

In one example implementation, subsystems represented by blocks mayinclude a flag that indicates that blocks in the subsystem are expectedto support mode-switched variable size signals. In an embodiment, thisflag can be provided as a widget on the block parameters dialog for thesubsystem. In another example, the flag indicator may be implemented asany control or setting associated with the block. In one embodiment,setting a flag for the subsystem may identify that all blocks within thesubsystem are capable of supporting mode-switched variable size signals.Such a flag may be used, at initialization of the system, to define thebehavior supported by the subsystem and its corresponding blocks.

For signal attributes such as dimensions, specialized propagation codemay be generated and provided with the executable code that allows for amode switch to be performed. Thereafter, a corresponding attribute maybe propagated in the deployed application, when executed (e.g., by ageneral-purpose computer system). In one example implementation,attributes can be determined before execution based on possible modechange event that may occur during execution. In such a case, executablecode need not include propagation functionality.

For an exemplary subsystem that has been setup to perform processing ofmode-switched variable size signals, the simulation engine may beconfigured to perform three analysis passes. The first analysis pass mayuse the constraint map described above that is provided within eachblock to determine the constraint map for the subsystem as a whole. Inan embodiment, this process may be performed recursively starting withhierarchically lowest subsystems (e.g., subsystems that do notthemselves contain other subsystems) first. This type of analysis passis illustrated in the example of FIG. 6B as discussed further below.

In the example of FIG. 6B, the constraint map for subsystem 610 may bedefined as:

Constraint1: Sizes of Out1 of subsystem 610 can be computed using sizesof In1 and In3

Constraint2: Sizes of Out1 of subsystem 610 can be computed using sizesof In2 and In3

Constraint3: Sizes of Out2 of subsystem 610 can be computed using sizesof In4

This constraint map may be derived from the constraint maps of blocks inthe Subsystem 610 (e.g., blocks 611, 616, etc.). Constraint maps candefine conditions that determine output port dimensions for theseblocks, and/or other attributes that can change in response to a modeswitching event.

According to one embodiment, the second analysis pass may define aSetOutputSizes function (as described for each individual block above)for subsystem 610 as a whole. Given one of the constraints from theconstraint map for subsystem 610, this method may set the output portsizes of subsystem 610 given the input port sizes that are identified asavailable by that constraint. This technique allows subsystem 610 to behierarchically subsumed by other subsystems, and therefore, blocksresponsive to mode events may be hierarchically arranged and theresultant hierarchy may be responsive to mode changes. For the exampleabove, this method may be defined as follows and may be embedded ingenerated code:

void SetOutputSizes(BlockHandle bh, int constraintIdx) {   if(constraintIdx == 1) {     bh->setOutputSizes(1, bh->getInputSizes(1) +    bh->getInputSizes(3));  } else if (constraintIdx == 2) {    bh->setOutputSizes(1, bh->getInputSizes(2) +    bh->getInputSizes(3));  } else {     assert(constraintIdx == 3);    bh->setOutputSizes(2, bh->getInputSizes(4));   } }Thus, additional code may be provided with subsystem 610 to handlesetting of output port sizes based on available input parameters.

According to one embodiment, a third analysis pass may determine onepropagation sequence for sizes within a subsystem marked as supportingvariable size signals. For example, this pass may involve a simple depthfirst traversal of all blocks inside a given subsystem. In oneembodiment, the pass may traverse all blocks starting at the subsysteminputs and using information about block connectivity (e.g., byfollowing block connectivity from inputs to outputs, or other scheme).According to one aspect, it is appreciated that this sequence may beused both in simulation and in the generated code to propagate all ofthe sizes within the subsystem when input sizes change in response to amode switch event. For the example above with respect to FIG. 6B, onepotential sequence for propagating sizes given new input sizes mayinclude the following sequences:

sum block 611

gain block 613

delay block 612

gain block 614

vector concatenate block 616

gain block 615

A further refinement to the above procedure may involve using theresults of the propagation pass in the third analysis phase above toperform optimizations on the SetOutputSizes function derived in thesecond analysis pass. For instance, if only a subset of constraints inthe constraint map of a subsystem are exercised in a given model, thenthe unused constraints for that subsystem can be optimized away leadingto a simpler SetOutputSizes function for subsystem 610.

During simulation or otherwise during any other execution of generatedcode, an event may be triggered that causes the sizes at the input ofthe subsystem (e.g., subsystem 610) to change. At this point, the sizesmay be repropagated through the subsystem using the propagation sequenceobtained in the third analysis pass described above. During thepropagation, a block's SetOutputSizes function (the third piece ofinformation specified by each block as described above) may be called tohelp propagate its sizes from its input to output or alternatively fromits output to its input.

Similarly, when code is generated for a subsystem, methods such as theSetOutputSizes functions as discussed above may be embedded into thegenerated code in accordance with the sequence defined by the thirdanalysis pass. This code may be invoked when the subsystem's sizes arechanged in response to an event.

Events that cause propagation of attributes may include explicitsignaling events such as those involving conditional subsystems. Forinstance, a subsystem that evaluates a condition and performs a functionas a result may be used to signal a mode change event. For instance, asubsystem having logic that implements a case switch function, do whileloop function, if else function or any other function whose executiondepends upon one or more parameters (e.g., an input signal). In anotherexample, an event could be generated from a block in a block diagramwhere the block behavior is specified or implemented in a textuallanguage, such as, for example, MATLAB or embedded MATLAB, amathematical script, etc. In another implementation, a mode switchingevent can include the occurrence of an exceptional or error condition,and attributes may be determined based on the occurrence of a particularexceptional or error condition.

According to one embodiment, a mode switching event can be generated bya number of different entities, including, but not limited to a user, anoperating system, an entity external to the system (e.g., a dataacquisition system, hardware, software, or combination thereof), orother entity. Further, a mode switching event may be generated in aconcurrent execution, for example, in a different task, process, orthread. Also, a mode switching event can be generated, for example, in adifferent simulation loop, by the operating system (for example, as partof an interrupt service routine), or can be based on user input.

Further, events may be non-hierarchical (e.g., not generated by a blockin the hierarchy) such as a broadcast event received from a modelingenvironment such as one generated by other programming environments(e.g., SimEvents® or Stateflow® environments of the Simulink® softwareproduct). Events may also be implicitly generated by changes in signalattributes to demarcated regions indicated as one that propagatesattributes. For instance, an implicit change in input signal parameters(e.g., size of the input parameter) may trigger a mode change event thatcan be propagated to other elements, blocks, subsystems, etc.

Mode change events that trigger a repropagation of signal sizes in asoftware package (e.g., the Simulink® software product) could beexplicit or implicit mode change events. Explicit events may includethose modeled by the user using conditional subsystems (e.g., as definedin the Simulink® software product) or through the use ofstate-transition diagrams (e.g., in the Stateflow® software product).For instance, a size repropagation can be triggered when a conditionalsubsystem such as an enabled subsystem or function-call subsystembecomes re-enabled.

One way to manage a mode change event in a graphical form may includeusing a state chart (e.g., a Stateflow® chart as provided in theStateflow® software product). Consider the system shown in FIG. 7, andits corresponding state chart shown in FIG. 8. In the example shown inFIG. 7, chart 701 may send a mode change event to subsystem 702. Inparticular, FIG. 7 shows a display of a chart 701 that provides modechange control input 703 to a subsystem 702 which can pass a value of aMODE_CHANGE_EVENT signal 704. Subsystem 702 may be, for example, similarto the subsystem 610 as shown in FIG. 6B.

In addition to control input 703, chart 701 may provide a number ofoutputs (y1, y2, y3, y4) to subsystem 702 as inputs (In1, In2, In3,In4). For instance, inputs In1, In2, In3, and In4 may correspond toinputs 617-620 of subsystem 601. Further, subsystem 702 may include oneor more outputs (e.g., Out1 705, Out2 706) that provide one or moreoutput signals, respectively. These may correspond to the outputs 621,622 of subsystem 601.

As shown in FIG. 8, a state chart 801 may be provided that indicatesthat a subsystem (e.g., subsystem 702) operates in one of two modes. Inthe example shown, these modes are referred to as Mode1 and Mode2. Chart701 sends a “mode change event” to subsystem 702 to initiate atransition from Mode1 to Mode2. According to one embodiment, the Mode1and Mode2 modes may use functional-form operators to set the sizes ofthe output data of the chart which are connected to subsystem 702. Thus,the sizes of the output data may depend on the mode change triggered bya chart (e.g., chart 801). More particularly, when the state transitiontakes place from Mode1 to Mode2 or vice versa, chart 801 may beresponsible for triggering a mode change event to a subsystem (e.g.,subsystem 702) which re-propagates the data sizes, sample times etc. orother attributes at the time of the event occurrence.

While this example shows chart 701 setting sizes of outputs to constantvalues, it is possible for the functional form operators (e.g., operatorsetSize( ) as shown in FIG. 8) to accept expressions evaluated atruntime or before runtime with results stored to be used during runtimefor setting the sizes. In addition, chart 701 can also set the types andsample times of the outputs via one or more functional form operators(e.g., operators such as setSampleTime( ) and setType( ). Thus, acapability may be provided to permit users to “explicitly” trigger themode changing based on runtime protocols using state diagrams inconjunction with a graphical programming environment.

Implicit mode change events may be triggered, for example, when sizes ofsignals feeding a mode-switched variable sizing subsystem may beexchanged at run-time. Such a size change may be automatically detectedby the subsystem which in turn may initiate a size repropagation and astate reset. This implicit detection of mode change could be added, forinstance, to any class of subsystems in the Simulink® software productor any other programming environment.

Although various embodiments may relate to propagating signaldimensions, it should be appreciated that other attributes may bepropagated to other elements in response to an event. For instance, anysignal attribute may be propagated, such as a data type of the signalbeing processed, a change in signal complexity, and sampling times usedfor processing a signal, among other attributes.

Further, although many of the examples described above may relate to theSimulink® software product, it should be appreciated that aspects may beapplied to other block-diagram modeling paradigms such as statetransition diagrams, discrete event modeling, and dataflow modeling.This is because the notion of attribute propagation in response to amode-switching events remains unchanged by the specific executionsemantics of a specific block-diagram modeling paradigm.

However, according to one embodiment, various aspects may be implementedin a graphical programming environment that uses blocks to representmodels. FIG. 9 shows an exemplary graphical programming environment inwhich blocks may be utilized to represent models according to oneembodiment. Environment 900 includes a block library block 910, aneditor 920, a simulator 930 and a code generator 940. Editor 920 andsimulator 930 may provide a graphical simulation and prototypingenvironment for modeling, simulating, and analyzing systems. Editor 920may incorporate blocks provided from block library 910 into systems tobe designed by users. Systems designed in editor 920 may be simulated bysimulator 930 to analyze the behavior of the designed systems. Exemplaryeditor 920 and simulator 930 may be found, for example, in the Simulink®software product.

As discussed, the block diagram programming environment enables one ormore users to design a block diagram corresponding to a modeled system,simulate the system's behavior, analyze the performance of the system,and refine the design of the system. The environment may also allowusers to design systems through a user-interface that allows drafting ofblock diagram models of the systems. Predefined blocks in block library910 may be made available to users when the users are building the blockdiagram of the systems to allow such users to more easily designsystems.

According to one embodiment, one or more block types in block library910 may be responsive to mode change events. Also, users may be providedtools to modify behavior of custom block types the users have created sothat such custom blocks are responsive to mode change events. In oneimplementation, a block may include logic that exhibits a change inexecution behavior in response to a mode change event.

In one embodiment, the user may be provided an interface thatselectively allows the user to define one or more functions orinstructions that can be performed responsive to a mode change event.For instance, a user dialog may be provided that permits the user toselect one or more predetermined functions that can be executedresponsive to the mode change event. For example, the user dialog maypermit a user to select an interpolation function, extrapolationfunction, first order hold function, zero padding function, resetvalues, or other function. In another embodiment, the user may bepermitted to define their own function that can be used, for example, tocompute output values and/or other attributes for a block responsive tothe mode change event. This may be accomplished, for example, bypermitting a user to define their own function, script, or procedurethat could be executed.

Individual users may be able to customize model blocks to: (a)reorganize blocks in some custom format, (b) delete blocks they do notuse, and (c) add custom blocks they have designed. The blocks may bedragged through some human-machine interface (such as a mouse orkeyboard) from block library 910 on to a window (e.g., a model canvas).The block diagram programming environment may include a block diagrameditor that allows users to perform such actions as draw, edit,annotate, save, and print out block diagram representations of systems.

The block diagram editor may be a graphical user interface (GUI)component that allows drafting of block diagram models by users. Theblock diagram programming environment may also provide a textualinterface with a set of commands that allow interaction with thegraphical editor. Using this textual interface, users may write specialscripts that perform automatic editing operations on the block diagram.The environment may also allow users an ability to simulate the designedsystems to determine the behavior of the systems. Further, theenvironment may include a block diagram execution engine that carriesout the task of compiling and linking the block diagram to produce an“in-memory executable” version of the model that may be used forgenerating code and/or simulating a block diagram model.

A block diagram generally includes a class of modeling formalisms thatconnect entities by relations. Semantics of a block diagram syntax canbe implemented to capture formalisms such as state transition diagrams,Petri nets, Kahn process networks, dataflow diagrams, sequence diagrams,Communicating Sequential Processes, and other syntactic and semanticmodels. The syntax of a block diagram may include any syntax typeincluding, but not limited to, squares, rectangles, circles, ovals,icons, and user defined syntax. Further, a graphical model such as ablock diagram may contain elements the behavior of which is completelyor partially determined by a textual language. This language may bedynamically typed and it may be array based. Also, the blocks may besoftware components, objects in a service oriented architecture,hardware intellectual property (IP) blocks, etc.

Block library 910 contains blocks of application specific models thatmay support the modeling and simulation of systems. Blocks in the blocklibrary 910 may be incorporated into models of the systems designedusing modeling and simulator 930. The blocks provided from the blocklibrary 910 may be represented generally by rectangular blocks accordingto one embodiment. However, other embodiments may represent elementswithin models using other techniques, such as graphical symbols and/ortextual symbols.

The model blocks provided by the block library 910 may include a blockprocessing block for selectively processing input data. According to oneembodiment, block library 910 may include Simulink® software productBlocksets, such as DSP blockset, Fixed-point Blockset and CommunicationsBlockset, commercially available from The MathWorks, Inc., Natick, Mass.The Simulink® software product Blocksets provide models and utilitiesfor the development and integration of models for target systems andsub-systems of the target systems.

According to one embodiment, code generator 940 may be capable ofgenerating source code for models that are responsive to mode changeevents. In one embodiment, code generator 940 generates customizableC-code directly from block diagrams of the models designed using editor920. Although it should be appreciated that C-language code may begenerated, it should be appreciated that any other type of code may begenerated. For example, Hardware Descriptive Language (HDL), ADA, Java,JavaScript, Python, Erlang, or other code types may be generated thatmay be graphical (e.g., UML diagrams). Alternatively and in addition,library or object code could be directly generated or referenced. Byautomatically generating source code, code generator 940 may enablerapid prototyping, hardware-in-the loop simulations, and desktop rapidsimulation on the models designed in the editor 920. Code generator 940may generate efficient source code for embedded systems applications. Itshould be noted that source code in FIG. 9 is an illustrative code thatmay be generated in the code generator 940, and that the code generator940 may generate different code for the models, such as Ada. Real-TimeWorkshop available commercially from The MathWorks, Inc., Natick, Mass.,is one example code generation tool that may be used as code generator940.

According to one embodiment, code generator 940 may be adapted togenerate a minimized source code responsive to mode change events. Inone embodiment, because additional code is provided that definesconstraints that reconcile how attributes are changed during runtime,the code that models a system can be created more efficiently, as thecode need not handle all conditions some of which may not necessarilyoccur. The smallest dimension of code may be determined, for example,through static or dynamic analysis (e.g., by executing a test suite).

One of skill in the art will appreciate that the graphical programmingenvironment 900 is not limited to block diagram programmingenvironments, but rather includes any other graphical programmingenvironments, such as state flowchart graphical programmingenvironments. For instance, the Stateflow® product, may provide agraphical environment for modeling and designing event-driven models.The Stateflow® product may enable users to generate state flowchartsthat graphically represent hierarchical and parallel states and theevent-driven transitions between the states of the models. The Simulink®software product, which may be interfaced with the Stateflow® product,may be used to execute the models and analyze the behavior of the modelsbased on, for example, state flowcharts created by the Stateflow®product.

Environment 900 may perform one or more processes with blocks thatpermit such blocks to exhibit behavior responsive to mode changes. Forinstance, FIG. 10A shows a process 1000 that may be implemented by anenvironment (e.g., environment 900) to graphically model, simulate andexecute code produced in accordance with various embodiments. At block1001, process 1000 begins. At block 1002, a graphical programmingenvironment (e.g., environment 900) may be presented to a user. Asdiscussed above, a graphical programming environment (e.g., a blockdiagram programming environment) may permit one or more users to designa graphical model corresponding to a modeled system, simulate thesystem's behavior, analyze the performance of the system, and refine thedesign of the system.

The environment may also allow users to design systems (e.g., at block1003) through a user interface that allows drafting of block diagrammodels of the systems. According to one embodiment, one or more blocksmay be provided that have the capability of propagating attributed inresponse to mode change events. Such blocks may be used to model asystem, that, when executed, exhibits different execution behavior inresponse to such mode change events.

Users may perform a number of different functions within the programmingenvironment on a modeled system. For instance, the user may simulate themodeled system (e.g., at block 1004) using, for instance, simulator 930.Such a simulation may include a graphical indication of mode changeevents in a display of a computer system. Further, a user may test codeassociated with the modeled system (e.g., at block 1006). Also, the usermay be capable of generating code (e.g., at block 1005) using thegraphical programming environment. As discussed above, a graphicalprogramming environment may provide a code generator (e.g., codegenerator 940) that is capable of generating executable code. Suchgenerated code may include one or more code elements responsive to modechange events as discussed above. The generated code may be executed byone or more systems at block 1007. As discussed above, such code may beexecuted by computer systems, devices, or any other system capable ofexecuting code. For example, a device capable of executing a model isdiscussed below with respect to FIG. 11.

FIG. 10B shows an example operation of a system capable of executing agraphical model. At block 1011, process 1010 begins. At block 1012, asystem, device or other entity capable of executing a model executescode associated with such a model at block 1012. The device may be, forexample, an embedded system that executes code produced, for example, bycode generator 940. At block 1013, it is determined whether a modeswitching event is received. As discussed above, the mode switchingevent may be generated, for instance, by a block in a model, or by anyother entity capable of generating an event. If a mode switching eventis received, the executed code may propagate one or more attributes atblock 1014. As discussed above, such attributes may be propagated toother blocks, subsystems, etc. of a modeled system. At block 1015, themodel is executed using the propagated attribute(s).

The system may receive further mode switching events that may cause thesystem, device or other entity to operate in one or more modes. Forinstance, the system may receive a further mode switching event thatcauses the system to return to a previous mode or to transition to oneof any number of additional modes. In such a case where a further modeswitching event is received (e.g., as determined at block 1016), thesystem may propagate one or more attributes associated with the event.

FIG. 11 is an exemplary electronic device 1100 that may be used forpracticing various aspects. Device 1100 may include a device thatexecutes instructions to perform one or more operations, such asexecuting a model, generating code, or executing code as discussed abovewith reference to FIGS. 10A-10B. Device 1100 may be, for example, ageneral purpose computing device such as a desktop computer, a laptopcomputer, a client, a server, a mainframe, a personal digital assistant(PDA), a web-enabled cellular telephone, a smart phone, smartsensor/actuator, or another type of device that executes instructions(e.g., an application specific appliance).

Electronic device 1100 includes a network interface 1130, a MODEM 1140,a secondary memory 1150, a primary memory 1160, a microprocessor 1170, amonitor 1180 and interface 1190. For example, interface 1190 may includeany type of single or multi-point computer interface such as, forexample, a keyboard, mouse, microphone, camera, touch screen,accelerometer, biometric or neural input, or any other type ofinterface. Microprocessor 1170 may control each component of theelectronic device 1100 to run code, such as software tools provided inthe graphical programming environment 900. Electronic device 1100 mayreceive data necessary for controlling the design and simulation of atarget system through, for example, the interface 1190. Received datamay include control data that may be used to set up operation modes of ablock processing block.

Monitor 1180 may display a result generated in the graphical programmingenvironment 1100. For example, monitor 1180 may display modeling resultsto one or more users. Primary memory 1160 may fetch codes from secondarymemory 1150 and provide the codes to the microprocessor 1170 codes. Thecodes may be executed by the microprocessor 1170 to operate theelectronic device 1100 and to run the graphical programming environment900. Secondary memory 1150 may contain software tools for applications.Secondary memory 1150 may include, in particular, code 1151 for theblock library 910, code 1152 for editor 920, and code 1153 for simulator930. Network interface 1130 and/or MODEM 1140 enable the electronicdevice 1100 to communicate with other electronic devices throughcommunication networks, such as Internet, intranet, LAN (Local AreaNetwork), WAN (Wide Area Network) or any other type of communicationnetwork. Further, communication facilities may support distributedimplementations of exemplary embodiments. In addition, code mayrepresent, for example, remote procedure calls and remote methodinvocations and the code may be based on service oriented architectures.

Although the examples above have been described relative to a Simulink®software products block diagram model, it should be appreciated thataspects may be practiced relative to models implemented in othergraphical modeling environments including UML modeling environments suchas the Rational Rose modeling environment available from InternationalBusiness Machines, Inc. of White Plains, N.Y. For instance, in UML,elements used in component diagrams, activity diagrams, and otherdiagram types may be capable of responding to mode switching events.Other graphical modeling environments may implement various aspects,including but not limited to, SimMechanics and SimElectronicsenvironments available from The MathWorks, the LabVIEW environmentavailable from National Instruments Corporation of Austin, Tex., SysMLavailable from SysML Partners at http://www.sysml.org, MaRTE OSavailable from the Universidad de Catabria, Spain, SCADE available fromEsterel Technologies, Mountain View, Calif., Modelica available from theModelica Association at http://www.modelica.org, Dymola available fromDynasim AB at http://www.Dynasim.se, AUTOSAR available from the AUTOSARdevelopment partnership at http://www.autosar.org, SystemC availablefrom the Open SystemC Initiative at http://www.systemc.org, CORBAavailable from the Object Management Group Inc. at http://www.corba.org,C++ available from a variety of vendors, among others.

CONCLUSION

Implementations may provide devices and techniques that propagateattributes in models. The foregoing description of exemplary embodimentsprovides illustration and description, but is not intended to beexhaustive or to limit the invention to the precise form disclosed.Modifications and variations are possible in light of the aboveteachings or may be acquired from practice of the invention. Forexample, while a series of acts has been described with regard to FIGS.10A-10B, the order of the acts may be modified in other implementationsconsistent with the principles of the invention. Further, non-dependentacts may be performed in parallel.

In addition, implementations consistent with principles of the inventioncan be implemented using devices and configurations other than thoseillustrated in the figures and described in the specification withoutdeparting from the spirit of the invention. Devices and/or componentsmay be added and/or removed from the implementations of FIGS. 5A-9 and11 depending on specific deployments and/or applications. Further,disclosed implementations may not be limited to any specific combinationof hardware.

Further, certain portions of the invention may be implemented as “logic”that performs one or more functions. This logic may include hardware,such as hardwired logic, an application-specific integrated circuit, afield programmable gate array, a microprocessor, software, wetware, or acombination of hardware and software.

No element, act, or instruction used in the description of the inventionshould be construed as critical or essential to the invention unlessexplicitly described as such. Also, as used herein, the article “a” isintended to include one or more items. Where only one item is intended,the term “one” or similar language is used. Further, the phrase “basedon,” as used herein is intended to mean “based, at least in part, on”unless explicitly stated otherwise. The scope of the invention isdefined by the claims and their equivalents.

1. A computer-readable medium comprising computer-executable instructions that when executed on a processor propagate attributes in a graphical model, the medium including: instructions for displaying a graphical model representing a system configured to operate using a first behavior, the graphical model comprising: a first element having a first attribute, a second element, and instructions for associating a mode switching event with the first element; instructions for: propagating the first attribute within the first element, or propagating the first attribute from the first element to the second element in response to the mode switching event; and instructions for executing the graphical model using the propagated first attribute to produce an execution result that reflects a second behavior of the graphical model.
 2. The computer-readable medium according to claim 1, wherein the at least one attribute comprises at least one signal attribute that includes at least one of a signal dimension, a signal data type, a signal complexity or a signal sample time.
 3. The computer-readable medium according to claim 1, further comprising instructions for selectively resetting a state associated with the at least one element in response to the propagating the at least one attribute.
 4. The computer-readable medium according to claim 1, wherein the mode switching event includes an explicit event or an implicit event.
 5. The computer-readable medium according to claim 1, wherein the mode switching event is generated by at least one of a state transition diagram, a discrete event diagram, or a block diagram.
 6. The computer-readable medium according to claim 1, wherein the first element includes at least one port, and wherein the mode switching event is in response to a change in attribute of a received signal associated with the at least one port.
 7. The computer-readable medium according to claim 1, wherein the graphical model includes at least one of a time-based block diagram or a dataflow diagram.
 8. The computer-readable medium according to claim 1, further comprising instructions for indicating that the at least one element propagates the at least one attribute in response to the mode switching event.
 9. The computer-readable medium according to claim 1, further comprising instructions for receiving a flag, the flag indicating that the first element can process the mode switching event.
 10. The computer-readable medium according to claim 1, wherein the first element includes at least one input port and at least one output port, and wherein the first attribute is a dimension, and wherein the computer-readable medium further comprises: instructions for receiving a map defining at least one constraint, the constraint identifying a dimension of the at least one input port, the dimension used to determine a dimension of the at least one output port; and instructions, responsive to a selection of the at least one constraint, for setting the dimension of the at least one output port based on the selected at least one constraint.
 11. A computer-readable medium comprising computer-executable instructions that when executed on a processor modify an operating mode for a system, the medium including: instructions for operating the system in a first mode having a first set of behavior; instructions for receiving a mode switching event; instructions for operating the system in a second mode having a second set of behavior based on the received mode switching event; and instructions, responsive to receiving the mode switching event, for executing the instructions for operating the system in the second mode.
 12. The computer-readable medium according to claim 11, wherein the computer-executable instructions are generated from a graphical model representing a modeled system.
 13. The computer-readable medium according to claim 12, wherein the graphical model comprises a first element having a first attribute and a second element, and wherein the computer-readable medium further holds: instructions for associating the mode switching event with a first element of the graphical model; and instructions for: propagating the first attribute within the first element, or propagating the first attribute from the first element to the second element in response to the mode switching event.
 14. The computer-readable medium according to claim 11, wherein the first set of behavior is operable to permit the system to process a first set of conditions by the system, and wherein the second set of behavior is operable to permit the system to process a second set of conditions by the system.
 15. The computer-readable medium according to claim 11, wherein the instructions responsive to receiving the mode switching event are executed by the system at runtime.
 16. The computer-readable medium according to claim 12, wherein the graphical model comprises a first element including at least one input port and at least one output port, and wherein the computer-readable medium further comprises: instructions for receiving a map defining at least one constraint, the constraint identifying a dimension of the at least one input port, the dimension used to determine a dimension of the at least one output port; and instructions, responsive to a selection of the at least one constraint, for setting the dimension of the at least one output port based on the selected at least one constraint.
 17. The computer-readable medium according to claim 12, wherein the graphical model comprises a first element having a first attribute, and wherein code associated with the first element is responsive to the received mode switching event.
 18. The computer-readable medium according to claim 17, wherein the code associated with the first model is capable of propagating the first attribute in response to the received mode switching event.
 19. The computer-readable medium according to claim 18, wherein the code is adapted to propagate the first attribute during execution of the code.
 20. A system comprising: a memory configured to store code representing a graphical model representing a modeled system, the graphical model having at least one element having associated code that is configured to propagate, through the element or to another element, at least one attribute associated with a port of the element; and a processor configured to execute the code, and responsive to a mode switching event, propagates the at least one attribute.
 21. The system according to claim 20, wherein the system operates in a first mode having a first set of behavior, and in response to receiving the mode switching event, the system operates in a second mode having a second set of behavior.
 22. The system according to claim 21, wherein the mode switching event is in response to a change in attribute of a received signal associated with the port of the element.
 23. A computer-readable medium comprising computer-executable instructions that when executed on a processor determine attributes in a graphical model, the medium including: instructions for displaying a graphical model representing a system configured to operate using a first behavior, the graphical model having a fixed model variable access structure and comprising: a first element having a first attribute; a second element having a second attribute; and instructions for associating a mode switching event with the first element; instructions for determining the second attribute to be consistent with the first attribute, the instructions for determining being responsive to the mode switching event; instructions for executing the graphical model using the determined second attribute to produce an execution result that reflects a second behavior according to the second attribute of the graphical model.
 24. The computer-readable medium according to claim 25, wherein the fixed model variable access structure is a fixed read structure.
 25. The computer-readable medium according to claim 25, wherein the fixed model variable access structure is a fixed write structure.
 26. The computer-readable medium according to claim 25, wherein the fixed model variable access structure is a fixed read and write structure.
 27. The computer-readable medium according to claim 25, wherein the fixed model variable access structure is a fixed compile-time structure.
 28. The computer-readable medium according to claim 25, wherein the instructions for determining propagate the first attribute to the second attribute.
 29. The computer-readable medium according to claim 25, wherein the instructions for determining further comprise instructions for solving at least one constraint associated with the first attribute and at least one constraint associated with the second attribute.
 30. The computer-readable medium according to claim 29, wherein the at least one constraint associated with the first attribute and the at least one constraint associated with the second attribute are related.
 31. The computer-readable medium according to claim 29, wherein the at least one constraint associated with the first attribute and the at least one constraint associated with the second attribute are a same constraint.
 32. The computer-readable medium according to claim 25, wherein the first element and the second element are not directly connected.
 33. The computer-readable medium according to claim 25, wherein the first element and the second element are connected via a nondirect feedthrough element.
 34. The computer-readable medium according to claim 33, wherein the nondirect feedthrough element comprises an input and an output, and wherein the nondirect feedthrough element does not have a direct relationship between the input and the output.
 35. The computer-readable medium according to claim 33, wherein the nondirect feedthrough element includes at least one of a group comprising: a delay element; a pre element; a shift element; and a memory element.
 36. The computer-readable medium according to claim 33, wherein the nondirect feedthrough element includes a filter block.
 37. The computer-readable medium according to claim 23, wherein the instructions for determining the second attribute include instructions that permit the user to define a process by which the second attribute is determined.
 38. The computer-readable medium according to claim 23, further comprising instructions that, when executed, display to a user an option to select a functionality that determines the second attribute responsive to the mode switching event.
 39. The computer-readable medium according to claim 23, wherein the at least one attribute comprises at least one signal attribute that includes a signal dimension.
 40. The computer-readable medium according to claim 23, wherein the at least one attribute comprises at least one signal attribute that includes a signal data type.
 41. The computer-readable medium according to claim 23, wherein the at least one attribute comprises at least one signal attribute that includes a signal complexity.
 42. The computer-readable medium according to claim 23, wherein the at least one attribute comprises at least one signal attribute that includes a signal sample time.
 43. The computer-readable medium according to claim 23, wherein the at least one attribute comprises at least one signal attribute that includes a signal invocation specification.
 44. The computer-readable medium according to claim 23, further comprising instructions for selectively resetting a state associated with the at least one element in response to the instructions for determining the at least one attribute.
 45. The computer-readable medium according to claim 23, wherein the mode switching event includes an explicit event.
 46. The computer-readable medium according to claim 23, wherein the mode switching event includes an implicit event.
 47. The computer-readable medium according to claim 23, wherein the mode switching event is generated by at least one of a state transition diagram, a discrete event diagram, a block diagram, a dataflow diagram, sequence diagram, scenario diagram, truth table, state transition matrix, entity flow diagram, queue/server network, and function block diagram.
 48. The computer-readable medium according to claim 23, wherein the first element includes at least one port, and wherein the mode switching event is in response to a change in attribute of a received signal associated with the at least one port.
 49. The computer-readable medium according to claim 23, wherein the graphical model includes at least one of a time-based block diagram, activity diagram, or a dataflow diagram.
 50. The computer-readable medium according to claim 23, further comprising instructions for indicating that the at least one element propagates the at least one attribute in response to the mode switching event.
 51. The computer-readable medium according to claim 23, further comprising instructions for receiving a flag, the flag indicating that the first element can process the mode switching event.
 52. The computer-readable medium according to claim 23, wherein the first element includes at least one input port and at least one output port, and wherein the first attribute is a dimension, and wherein the computer-readable medium further comprises: instructions for receiving a map defining at least one constraint, the constraint identifying a dimension of the at least one input port, the dimension used to determine a dimension of the at least one output port; and instructions, responsive to a selection of the at least one constraint, for setting the dimension of the at least one output port based on the selected at least one constraint.
 53. A computer-readable medium comprising computer-executable instructions that when executed on a processor modify an operating mode for a system, the computer-executable instructions being generated from a graphical model representing the system, the graphical model having a fixed model variable access structure, the medium including: instructions for operating the system represented by the graphical model in a first mode having a first behavior; instructions for receiving a mode switching event; instructions for operating the system in a second mode having a second behavior based on the received mode switching event; and instructions, responsive to receiving the mode switching event, for executing the instructions for operating the system in the second mode.
 54. The computer-readable medium according to claim 53, wherein the graphical model comprises a first element having a first attribute and a second element, and wherein the computer-readable medium further holds: instructions for associating the mode switching event with a first element of the graphical model; instructions for representing a first element having a first attribute; instructions for representing a second element having a second attribute; and instructions for associating a mode switching event with the first element; instructions for determining the second attribute to be consistent with the first attribute, the instructions for determining being responsive to the mode switching event.
 55. The computer-readable medium according to claim 53, wherein the fixed model variable access structure is a fixed read structure.
 56. The computer-readable medium according to claim 53, wherein the fixed model variable access structure is a fixed write structure.
 57. The computer-readable medium according to claim 53, wherein the fixed model variable access structure is a fixed read and write structure.
 58. The computer-readable medium according to claim 53, wherein the fixed model variable access structure is a fixed compile-time structure.
 59. The computer-readable medium according to claim 54, wherein the instructions for determining are adapted to propagate the first attribute to the second attribute.
 60. The computer-readable medium according to claim 54, wherein the instructions for determining further comprise instructions for solving at least one constraint associated with the first and second attributes.
 61. The computer-readable medium according to claim 54, wherein the first element and the second element are not directly connected.
 62. The computer-readable medium according to claim 54, wherein the second element includes a nondirect feedthrough characteristic.
 63. The computer-readable medium according to claim 54, wherein the first element and the second element are connected via a nondirect feedthrough element.
 64. The computer-readable medium according to claim 62, wherein the nondirect feedthrough element comprises an input and an output, and wherein the nondirect feedthrough element does not have a direct relationship between the input and the output.
 65. The computer-readable medium according to claim 62, wherein the nondirect feedthrough element includes a delay block.
 66. The computer-readable medium according to claim 62, wherein the nondirect feedthrough element includes a memory block.
 67. The computer-readable medium according to claim 54, wherein the instructions for determining the second attribute include instructions that permit the user to define a process by which the second attribute is determined.
 68. The computer-readable medium according to claim 54, further comprising instructions that, when executed, display to a user an option to select a function that determines the second attribute responsive to the mode switching event.
 69. The computer-readable medium according to claim 53, wherein the first behavior is operable to permit the system to process a first set of conditions by the system, and wherein the second behavior is operable to permit the system to process a second set of conditions by the system.
 70. The computer-readable medium according to claim 53, wherein the instructions responsive to receiving the mode switching event are executed by the system at runtime.
 71. The computer-readable medium according to claim 53, wherein the graphical model comprises a first element including at least one input port and at least one output port, and wherein the computer-readable medium further comprises: instructions for receiving a map defining at least one constraint, the constraint identifying a dimension of the at least one input port, the dimension used to determine a dimension of the at least one output port; and instructions, responsive to a selection of the at least one constraint, for setting the dimension of the at least one output port based on the selected at least one constraint.
 72. The computer-readable medium according to claim 53, wherein the graphical model comprises a first element having a first attribute, and wherein code associated with the first element is responsive to the received mode switching event.
 73. The computer-readable medium according to claim 72, wherein the code associated with the first model is capable of propagating the first attribute in response to the received mode switching event.
 74. The computer-readable medium according to claim 73, wherein the code is adapted to propagate the first attribute during execution of the code.
 75. A system comprising: a memory configured to store information representing a graphical model representing a modeled system, the graphical model having a fixed model variable access structure and including at least one element, the at least one element having associated code that is configured to make at least one attribute associated with a port of the element consistent another attribute of the at least one element or another element; and a processor configured to execute the code, and responsive to a mode switching event, defining the at least one attribute to be consistent with the another attribute.
 76. The system according to claim 75, wherein the system operates in a first mode having a first behavior, and in response to receiving the mode switching event, the system operates in a second mode having a second behavior.
 77. The system according to claim 76, wherein the mode switching event is in response to a change in attribute of a received signal associated with the port of the element.
 78. The system according to claim 75, wherein the attribute is propagated through the at least one element or to another element.
 79. The system according to claim 75, wherein the fixed model variable access structure is a fixed read structure.
 80. The system according to claim 75, wherein the fixed model variable access structure is a fixed write structure.
 81. The system according to claim 75, wherein the fixed model variable access structure is a fixed read and write structure.
 82. The system according to claim 75, wherein the fixed model variable access structure is a fixed compile-time structure. 